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activities of slashers, who cut down
trees and undergrowth is, not
surprisingly, called Slash. The
forestry people would normally like
this to rot naturally, but many
farmers disagree and burn it instead.
Because it is both extensive and
inaccessible, helicopters are used to
set the whole lot on fire, but only in
temperatures above freezing, and
below 45 kts, from somewhere
between 150-300 feet. This
technique may also be used when
fighting forest fires:
·  Temporarily knocking down
large smoke columns so Air
Tankers can see where they’re
going, by igniting strips of
forest within about 10-30
metres of, and parallel to, an
active flame front, which starves
it of oxygen. Depending on fuel
types, temperature, dewpoint,
wind velocity, etc. this can last
up to around 20 minutes.
·  Prevention. Forests can be
torched around priority areas,
such as towns or gas plants to
get rid of anything that might
burn later in the fire season.
·  Back burning, when a rapidly
advancing fire is moving
towards a cut line, or natural fire
break, like a creek, although this
could also be done on initial
attack. Parallel strips ignited
between the fire front and the
intended firebreak will
drastically diminish a fire’s
momentum, decreasing its
likelihood to spot across the
firebreak, and keep going, so the
firebreak can be used as a
defensive line. In other words,
the idea is to remove fuel from
the path of a rapidly moving
fire, where the head creates a
powerful convective column
that pulls air in from all sides,
including downwind. When this
flow is steady, a fire is started
ahead of the main fire from a
natural barrier, such as a road or
river, which is sucked in and
creates a wider firebreak
·  Aiding in ground crew mop up,
by burning off unburned areas,
making it safer. Ragged edges
can also be straightened, to
reduce the perimeter and
decrease workload.
·  Reducing the time, effort, and
expense of cutting fire
perimeters for fires with many
fingers, which is very time
consuming.
·  Steering a fire somewhere.
You might carry a drip torch
beneath your machine and get to
become an instant pyromaniac with
a 20-foot flame about 20-25 feet
below the cargo hook, carrying a 55-
gallon fuel drum, associated pipes,
wiring, etc., and a fire extinguisher to
cope with hang fires, or those that
start around the valve outlet when it
closes. Apart from danger to the
helicopter, the mixture could fall off
and start unwanted fires.
The equipment weighs about 550 lbs
when full, and can use straight Jet
Fuel, or have it mixed with a gelling
48 The Helicopter Pilot’s Handbook
agent, which makes it cling to foliage
and be more effective (I love the
smell of Petrogel in the morning).
There will be a propane flame for
ignition. As there is a polarityswitching
feature, aircraft rewiring is
unnecessary and, although it
demands a 25-amp circuit breaker,
30 amps is recommended.
Another way is to use polystyrene
balls about an inch across, full of
Potassium Permanganate, injected
with Ethylene Glycol (anti-freeze) in
a special dispenser and ejected from
the aircraft. For maximum safety, the
balls should not ignite inside ten
seconds, but most take about thirty.
On larger fires, an intermediate
helicopter will be dedicated for the
job, on short standby and used for
little else, except when prevailing
conditions are not conducive to
burning, and you may be assigned to
other flying duties.
Always expect a Forestry Officer to
be on board.
Your maximum speed is whatever
you can control, after Flight Manual
limitations, so burning fuel reaches
the ground at about 15 kts. If you go
too fast, say over 20, the mixture will
be too lean and the fuel will be used
up before reaching the ground.
When greater than translation, fuel
will recirculate to give a poor
pattern, aside from damaging the
equipment.
Otherwise, common-sense rules
apply, such as keeping the helicopter
(or the mixing area) well away from
buildings, etc. on the pad, grounding
everything, wear flameproof or
resistant clothing and equipment, or
at least cotton protective clothing,
brief anything that moves, etc. Don't
forget equipment spares, and to fly
　
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本文鏈接地址：The Helicopter Pilot’s Handbook(32)